Force switches and force sensing membranes are used in various applications to detect contact/touch, detect and measure a relative change in force or applied load, detect and measure the rate of change in force, and/or detect the removal of a force or load.
Force switches and force sensing membranes typically function by detecting a signal when otherwise separated conductive films, electrodes, or circuits are brought together under the application of force by a user.
Force sensing membranes, for example, typically consist of an elastomer comprising conductive particles (the “elastomeric layer”) positioned between two conducting contacts. When pressure is applied to one of the conducting contacts, the conducting contact is pressed against the surface of the elastomeric layer, and conduction paths are created. The conduction paths are made up of chains of the conductive particles that make a tortuous path through the elastomer. Therefore, the concentration of conductive particles in the elastomer must be above a certain threshold (that is, above the percolation threshold) to make a continuous path. As pressure is increased, greater numbers and regions of contact between the conducting contact and the elastomeric layer's surface are created. Thus, a greater number of conduction paths through the elastomer and conductive particles are created, and the resistance across the elastomer layer is decreased.